Supplemental inflatable restraint (SIR) systems for automotive vehicles incorporate a squib which is fired upon detection of a crash condition to rapidly inflate one or more air bags for occupant protection. Frontal SIR systems are well known for protecting against frontal collisions, and side systems have been proposed for protection against side impacts. For the frontal systems, an accelerometer is used to sense the vehicle deceleration and a control circuit, generally a microprocessor, evaluates the accelerometer output to determine whether a bag mounted in the steering wheel or dashboard should be inflated. Typically, the determination to deploy a bag is made in two stages: first when the accelerometer output reaches a given threshold value an impending crash is identified and in response the deployment system is armed, and second, the accelerometer output is further analyzed to determine the severity of the impact and a deploy command is generated when a given severity level is reached. Side SIR systems employ an air bag and an accelerometer on each side of the vehicle for independent response to lateral impact, and the deployment decision is made in much the same way as for the frontal system.
An important difference between the frontal and side SIR systems is in the required time for response. Because of the distance between the front of a vehicle and the passenger compartment, there can be a significant time between frontal impact and the start of bag inflation; a side impact, on the other hand occurs close to the passenger compartment and bag inflation must begin in a much shorter time. Another difference is that while separate accelerometers are used for each system, some control and deployment circuitry can be shared to avoid the expense of duplication of hardware. In particular, the microprocessor of the frontal system processes the frontal accelerometer signals to generate a deploy command and also carries out the deployment. It also does some diagnostic functions and controls warning indicators.
It is proposed to utilize the control functions of the frontal microprocessor to service the side SIR system. In that case it is essential that communication between the side system and the frontal processor be extremely reliable and not subject to false deployment commands due to noise or other causes. It is also essential that the communication be effected at high speed and that the speed or efficiency of the frontal processing should not be significantly affected.
It is known to use 8 bit serial communication for linking electronic modules in vehicles. To accomplish the communication speed and robustness required in the SIR system, clock speeds in the megahertz range are required. Implementation of that technology would necessitate expensive data handling hardware at each side sensor and at the frontal processor.